1. Field of the Invention
The present invention relates to a system for the high speed reading of a charge transfer matrix optical sensor organized with one stroke frame transfer for the video detection of brief images. The use of the invention is more particularly contemplated for a multichannel reading system of optical signals using a streak camera.
2. Description of the Prior Art
Detection matrices are known formed as a solid charge transfer circuit used for transferring television image frames. For example, the sensor TH 7861 of THOMSON-CSF is organized for effecting the frame transfer to the TV standard CCIR, it comprises 576 lines of 384 points. This known matrix structure includes a photosensitive zone and a storage zone, each of 288 lines. After integration and exposure for the duration of a frame, namely 20 milliseconds for 25 images/second, the corresponding information is transported from the photosensitive zone to the storage zone where it is reread at the television rate through a reading register whereas the second frame offset by a line for providing interlacing is integrated in the photosensitive zone. With such a sensor an image can be read formed of two frames during a total time of 40 milliseconds in accordance with the television standard.
For a higher speed image analysis corresponding to much shorter phenomena, the photosensitive matrix is organized differently. This is the case of the TH 7882 of THOMSON-CSF which is derived from the above mentioned device and which is constructed with the same technology but the storage zone is also photosensitive. This configuration gives a large photosensitive area formed of 576 lines of 384 elementary points or pixels. This sensor can only be used in the one stroke mode; after integration, it must be placed in the darkness and the image may be read at any rate, provided that it is compatible with the integration of the dark current of the photosensor, and with the pass band of its internal circuits and its output amplifier. This solution has however limitations. The integration and reading times are limited by the increase of the dark current due to thermal effects. At 25.degree. C., this limitation is of the order of 100 to 500 milliseconds. A minimum reading time of 25 milliseconds results from the maximum foreseeable frequency for the reading control signals also called reading phases.
Such a time is too long for the analysis of very brief phenomena. For the invention phenomena are contemplated which may for example be the order of 1 millisecond and which are not repetitive.
One solution would consist in using the above one stroke matrix in a reduced part of its photosensitive zone by reducing the number of pixels of the image sufficiently for reducing the time for reading the image. This solution is however not satisfactory for the resolution of the image is seriously degraded thereby.
The solution proposed by the invention allows these very brief times to be obtained as well as the optimum resolution for the image corresponding to the whole of the points of the matrix.